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Technical Discussions
Ken Heaps
Ken Heaps
08:21 Oct-07-2010
Intrinsically safe UT thickness gauge with A-scan

I have been tasked with finding, qualifying, then procuring an intrinsically safe UT machine that has an A-scan display (no D-meters). My research indicates only one model, the Krautkramer USN 23 ex, meets this criteria, and that it has been discontinued. I have located some for purchase but find the seller unable to answer technical questions regarading qualification. The qualification would consist of two steps.
1. Can the unit detect a 1/16" (1.58mm) diameter flat bottom hole at about 0.100" (2.54mm) metal path?
2. Is the rep rate fast enough to detect the above indication as a scan speed of 4" (102mm) per second?
I would much appreciate any feedback from folks who have hands on experience with this unit, know of another intrinsically safe unit, or have any other comments on the unit or the qualification criteria.

 
 Reply 
 
S V Swamy
Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex , India, Joined Feb 2001, 787

S V Swamy

Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex ,
India,
Joined Feb 2001
787
10:24 Oct-07-2010
Re: Intrinsically safe UT thickness gauge with A-scan
In Reply to Ken Heaps at 08:21 Oct-07-2010 (Opening).

Dear Ken,

I am intrigued by the qualification - intrinsically safe. Safe in what conditions?

Coming to the qualification criteria, the metal path for the hole appears rather less and the separation between the surface echo and the reflected echo from the bottom of the hole may be poor. So, you should actually check it out or ask the seller to give you screen shots.

Normally PRF is linked to the range and most of the flaw detectors are designed for scan rates higher than that. Also, whether the scan rate is independently adjustable needs to be confirmed.

I have not worked with the particular model and my comments are hence general.

Regards

Swamy

 
 Reply 
 
Roger Duwe
NDT Inspector, API-510, 570, 653
MISTRAS, USA, Joined Jan 2009, 148

Roger Duwe

NDT Inspector, API-510, 570, 653
MISTRAS,
USA,
Joined Jan 2009
148
20:42 Oct-11-2010
Re: Intrinsically safe UT thickness gauge with A-scan
In Reply to S V Swamy at 10:24 Oct-07-2010 .

Sorry, but no UT flaw detector can be "intrinsically safe" per the NFPA definition. The problem is the pulser. If you will go into a dark room and, with the machine running, unscrew the transducer, you will see a small blue spark. Pulser voltage is typically 100 - 200 volts. It will make a spark.

I usually skirt the issue by taking an Air Monitor with me. If there is no flammable gasses present -- Lower Explosive Limit "LEL" -- then Intrinsic Safe is a moot point. Additionally, the remainder of the machine is low voltage. If the probe pulser circuit is never disconnected, there is no exposure. Plus, the pulser [transducer] cable is shielded and the shield is grounded.

 
 Reply 
 
John O'Brien
Consultant, -
Chevron ETC , USA, Joined Jan 2000, 280

John O'Brien

Consultant, -
Chevron ETC ,
USA,
Joined Jan 2000
280
19:12 Oct-12-2010
Re: Intrinsically safe UT thickness gauge with A-scan
In Reply to Ken Heaps at 08:21 Oct-07-2010 (Opening).

There are multiple parts to your question. It looks like you wnat to make thickness readings which is easier than flaw detection. Cygnus and I believe Dakota Instruments both make thickness gauges and may be now producing items with A Scan displays. You need to define the IS zone area Zone 1 Div 1 is more difficult and whether you accept ATEX over the UL from the US. To certify disconnectable probes without sparking is the issue as discussed by Roger which limits choices.

Rental companies like Ashtead do rent USN 23 so you could rent one and test on blocks before committing to a purches.

You should also challenge if you really need IS certification. Good procedures, gas detectors and not disconnecting probes with unit switched on should all allow you to operate successfully in an hazardous area - its done all ove rthe world every day.

 
 Reply 
 
Phil Harper
Director, Tribosonics
Tribosonics Ltd, United Kingdom, Joined Feb 2004, 10

Phil Harper

Director, Tribosonics
Tribosonics Ltd,
United Kingdom,
Joined Feb 2004
10
08:54 Oct-20-2010
Re: Intrinsically safe UT thickness gauge with A-scan
In Reply to John O'Brien at 19:12 Oct-12-2010 .

Hi Guys,

Intrinsically safe is very difficult to do as it is the most restrictive of the ATEX certifications. It is not, however, impossible - you just need new technologies.

We are in the process of developing a IS ultrasonic monitoring tool for Zone 1 Div 1 (strictly speaking not a NDT device). We're just in the stages of assembling and testing our first prototype device and will then be applying for ATEX and UL certification. This platform might be suitable for your requirements if you can wait a bit and if we can design it to suit your needs. For example we're having a 10 kHz rep rate (as an asside we have another instrument here (non-IS) that will do 100 kHz rep rate!).

Get in touch if you would like to know more.

Phil.

 
 Reply 
 
David Bunch
David Bunch
19:03 Nov-04-2010
Re: Intrinsically safe UT thickness gauge with A-scan
In Reply to Roger Duwe at 20:42 Oct-11-2010 .

On the thickness meters I have used, you cannot unscrew the transducer. They are fused with the cable to form a single piece. Usually they have a two or three pronged plug that pushes into the thickness meter.

 
 Reply 
 

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